Acoustic reflex ear protective system



Dec. 11, 1962 J. FLETCHER ETAL 3,068,319

AcoUsTTc REFLEX EAR PROTECTIVE SYSTEM 2 Sheets-Shes?l 1 Filed NOV. 4,1960 Decu, 1962 J. L.. FLETCHR ETAL 3,063,319

ACOUSTIC REFLEX EAR PROTECTIVE SYSTEM Filed Nov. 4, 1960 2 Sheets-Sheet2 1". ,v, lill hun NW y MP-4u 1N VEN TORS Jamv FLETCHER ma# J, R/QPFLLEl@ Patented ec. l1, 1962 ffice 3 068,319 ACGUSTIC REFLEX AR PRQTECTIVESYSTEM John L. Fletcher, U.S. Army, Fort Knox, Ky., and Arthur J.Riopelle, Yerker Labs., @range Park, Fla. Filed Nov. 4, 1960, Ser. No.67,443 5 Claims. (Cl. 179-1) (Granted under Title 35, U.S. Cod-e @952),sec. 2651) The invention described herein may be manufactured and usedby or for the Government for governmental purposes without the paymentof any royalty thereon.

The present invention relates to an acoustic reflex ear protectivesystem and more particularly to an acoustic refiex ear protective systemfor introducticn of a sound to the ear anticipatory to the reception ofa second sound to the ear such that the ear is protected fromnoiseinduced hearing loss.

The introduction of a sound at the level of 80 to 110 decibels, forexample, into the human ear causes a brief contracture of the stapediusand tensor tympani muscles of the middle ear and tightens the eardrum.The tightened eardrum is less free to vibrate and thus less able totransmit sound vibrations to the fluids of the inner ear. Thiscontracture is termed the acoustic reiiex.

A system exemplary of the present invention may include a source ofenergy, a pair of energy paths connected in parallel to the source,sonic generator means connected to each path and actuated by the energysource, and energy impeding means positioned in one path between thesonic generator means and the energy source such that actuation of onesonic generator means precedes actuation of the other sonic generatormeans by the energy source whereupon the sound produced by therst-actuated sonic generator means conditions by acoustic reflex the earfor reception of the sound produced by the last-actuated sonic generatormeans,

An object of the present invention is to provide a new and improvedacoustic reflex ear protective sysem.

Another object is the provision of an ear protective system to induce asound to the ear to actuate acoustic reflex in advance of the receptionof sound which otherwise could cause noise-induced hearing loss.

Still another object of this invention is to provide a system includingcircuitry adapted for use with standard military equipment.

A further object is the provision of an ear protective system whichcauses delay of the production of a deafening noise until after theproduction of a sound capable of conditioning by acoustic reiiex the earfor reception of the deafening noise.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawing in which like referencenumerals designate like parts throughout the figures thereof andwherein:

FIG. 1 is a block diagram of the general concept of the invention;

FIG. 2 illustrates in schematic circuitry a portion of a preferredembodiment of the system disconnected from an input section of an audiofrequency ampliiier; and

FIG. 3 is a view of the specific circuitry of the input section of anaudio frequency amplifier connected with the output of an oscillatorsection of the system.

Referring to FIG. 1 there is shown a voltage supply 11 connected to afiring trigger or switch 12 which is in series with a delay section 13of the protective system. The output of the delay section 13 is fed to afiring solenoid 14, which, when energized upon closing of the switch 12,actuates by mechanical linkage not shown, the firing mechanism of a gun15, for example.

An oscillator section 20 illustrated in FIG. l is connected in parallelwith the delay section 13 to the switch 12, as best shown in FIG. 3,with an output terminal 17 connected to the input point 18 of an audiofrequency amplifier and mixer 19, FIG. 1. The amplifier and mixer 19 isidentified as AM-65/ GRC by the U.S. Army, and is described in detail inTechnical Manual 11-5039, an Army Signal Corps publication availablefrom the U.S. Army Publications Branch, Ofiice of The Adjutant General,the Pentagon, Washington 25, D.C.

Basically, the audio frequency amplifier and electronic mixer 19includes three channels 21 and is designed to provide interphoneoperation and radio monitoring in installations using one or tworeceiver-transmitters and one or more interphone control boxes. Theinstallation shown in FIG. l includes, for example, a radioreceivertransmitter 22, designated by the U.S. Army as RT-70/GRC, whichis used for radio and interphone operation. The radioreceiver-transmitter output is fed to input 23 of the amplifier andmixer 19. Input 24 of the amplifier and mixer 19 is used for a radioreceiver and interphone, generally designated as numeral 25. Input 26 isavailable for intercommunication only between local stations, and has aparallel connection which serves as the input point 18 from theoscillator section 16. Control boxes 27 are selectively connected bythree-position switches 28 to output channels 21 of the amplifier andmixer 19 and are in turn serially connected to headsets 31. The controlboxes 27 are identified as C-375/VRC by the U.S. Army in TM 11-5039,referred to hereinabove. Y

As shown best in FIG. 2, the oscillator section 16 of the ear protectivesystem includes the output terminal 17 connected to an output volumecontrol 29 of an oscillator 31, FIG. 3. A relay 32 with pairs ofcontacts 33 and 34 has its actuating coil 35 operatively connected tothe voltage supply 11 at terminals 36 by the trigger or switch 12. Therelay 32 is actuated to close contacts 33 to complete a circuit from theoscillator 31 to an input section 37 of the audio frequency amplifier19. Also, actuation of the relay 32 closes the contacts 34 to complete acircuit from the supply 11 to ground through a relay 38 which in turncloses contacts 39 to complete the connection between the oscillator 31and the audio amplifier 19.

The oscillator 31, FIG. 3, is a conventional R.C. coupled transistoroscillator, and, in the preferred embodiment of the invention, isdesigned with an output of approximately one volt at 1000 cycles persecond. The oscillator 31 is powered by a 22.5 volt battery 41, forexample, with the oscillator output appearing at terminal 17, which isconnected through the output volume control 29 to the input point 1S ofthe amplifier 19.

A circuit for energizing the solenoid 14 is shown in FIG. 3 to includerelays 42 and 43 in series arrangement having pairs of contacts 44 and45 with coils 46 and 47, respectively. The relays 42 and 43 connect thesolenoid 14 with the switch 12 and the voltage supply 11, and are inparallel with the relay 32. A charging capacitor 48 and a variableresistor 49 are provided for delaying the actuation of the solenoid 14by the source 11.

Cannon sockets 51 are utilized in the schematic views of the system inFIGS. 2 and 3 as terminal blocks.

Operation The firing trigger 12, which may be a hand gripped electricalswitch, is closed by an operator whereupon 24 volts, for example, areapplied from the voltage supply 11 to the charging capacitor 48 and thevariable resistor 49. The current sensitive relay 42 has its coil 46energized upon charging of the microfarads, capacitor 4S for example, atwhich time the contacts 44 of the relay 42 complete the circuit forenergizing the relay 43. Through aoeasra Ei the closing of the contacts45 of the relay 43, the 24- volt circuit is completed to the solenoid14, causing a gun 15, for example, to fire.

Also, when the iiring trigger 12 is closed, 24 volts from the supply 11are applied to the relay 32, energizingthe coil 35 and causing the twosets of contacts 33 and 34 to close. The closing of contacts 34energizes the relay 38 in the input section 16 of the amplifier 19 tocomplete an input circuit, and the closing of contacts 33 completes thecircuit from the output terminal 17 of the oscillator 3l to the inputpoint 18 of the amplifier 19. The output of the amplifier 19 isdistributed to one or more 0f the controlboxes 27 and is then fed intoearphones 31 worn by an operator to cause an acoustic reflex in hisears. The delay in the firing circuit caused by the charging capacitor48 is sufiicient to permit reception of the output signal from theamplifier 19 into the ear of an operator through headsets 31 lprior tothe energization of the solenoid 14 which causes a gun 15 to iire, forexample. Accordingly, the ears of the operator are protected from thedamaging effect of the gun noise by activation of the acoustic reflex bythe output of amplifier ,19 in advance of the tiring ofthe gun.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. For example, the relay43 may be omitted if the contacts 44 of the relay 42 are capable ofcarrying the 6 ampere current, in the preferred embodiment, necessary tooperate the firing solenoid 14. Similarly, the audio amplifier 19 may beomitted fromrthe ear protective system should the output power of theoscillator 31 be suliicient to deliver the acoustic energy required tocreate acoustic reex in the human ear. `It is therefore to beunderstood, that within the scope of the teachings herein, the inventionmay be practiced otherwise than as specifically described;

We claim:

l. An acoustic reiiex ear protective system for protection against adistressing sound the timing of` which distressing sound is subject tocontrol comprising an energy source, a plurality of energy pathsconnected in parallel to said energy source, control means for saidenergy source, means for generating said distressing sound and means forgenerating non-distressing sound stimuli, each of said sound generatingmeans positioned in one of said energy paths and actuated by the energysource, and sound delay means connected serially between saiddistressing sound generating means and said energy source, whereby theenergy source actuates said nondistressing sound generating means inadvance to the actuation of said distressing sound generating means.

2. An acoustic reflex ear protective system comprising a source ofelectrical energy, a pair of sound generators connected in parallel tothe source and actuated thereby, one of said sound generators being forproduction of distressing sound the other of said generators being forproduction of non-distressing sound stimuli, means for interrupting theconnection between the source and the generators, and electrical delaymeans connected serially between the distressing sound generator and thesource whereby said non-distressing generator is actuated in ad.- vanceof the distressing sound generator upon connection with the source,

3. An acoustic reflex ear protective system `which comprises a source ofelectrical' energy; a first circuit connection to the source includingan oscillator with an output of frequency within the audible range,transducer means connected to the output of the oscillator forconverting the output signal to sound energy of an intensity to effectacoustic reflex in the human ear, and means for interrupting theconnection between the oscillator and the transducer connectedoperatively to the source of electrical energy; and a second circuitconnected to the source in parallel with the tirst circuit and includinga source of sound energy, means for actuating the souce of sound energyconnected serially between the source of sound energy and the source ofelectrical energy and energized by the latter source, and an electricaldelay means connected serially between the actuating means and thesource of electrical energy; and means for interrupting the connectionbetwen the electrical source and therparallel circuits whereby uponcompletion of the connection the first circuit produces a sound tocondition the ear by acoustic reflex prior to the production of sound bythe source in the second circuit by a time period determined by thedelay means in the second circuit.

4. An acoustic reflex ear protective system comprising an -oscillatorfor generating an audio frequency signaLa transducer connected to theoutput of the oscillator for production of a sound of an intensity tocause acoustic reflex in the human ear, a first relay having contactsfor interrupting the connection between the oscillator and thetransducer, a voltage source operatively connected to the first relayfor actuating the contacts, a delay relay connected in parallel with therst relay to the voltage source, a solenoid connected in series withcontacts of the delay relay and actuated by the voltage source up:npassage of the current from the voltage source through the contacts ofthe delay relay, sound producing means connected operatively to thesolenoid and energized thereby for production of a sound of higherintensity and diterent frequency than that of the output signal of thetransducer, and a switch for connecting the relays with the voltagesupply whereby when the switch is closedthe transducer output soundconditions the ear by acoustic reiiex in advance of the production ofthe sound by actuation of the solenoid.

5. An acoustic reflex ear protectivesystem comprising an oscillator forgenerating an audio frequency signal, a voltage supply for driving theoscillator, an audio amplifier connected to the output of the osci latorfor amplifying the signal, an earphone connected'to the output of theamplifier for converting the amplified signal to a sound of an intensityto etect acoustic reflex in the ears of a listener from the earphone, airst'relay having contacts for interrupting the connection betweentheoscillator and the amplifier, a gun having a solenoid-actuatedtrigger mechanism, a trigger switch, adelay relay having contactsconnecting the solenoid with the trigger switch, a switch, the tirstrelay being connected to the switch in parallel with the ldelay relay,and a voltage source connected to the switch for energizing'the delayrelay, the solenoid, and the contacts of the iirst relay.

References Cited in the file of this patent UNITED STATES PATENTS2,942,070 Hammond et al. Y June 2l, 1960

